Research Report                                      Age-Related Changes in Strength,                                     ...
Age-Related Changes in Strength, Joint Laxity, and Walking PatternsS      ymptomatic knee osteoarthritis      in the prese...
Age-Related Changes in Strength, Joint Laxity, and Walking PatternsTable 1.Group Characteristics                          ...
Age-Related Changes in Strength, Joint Laxity, and Walking PatternsSkeletal alignment of the tested limb            tion w...
Age-Related Changes in Strength, Joint Laxity, and Walking Patternsplate data. Sagittal- and frontal-plane       contracti...
Age-Related Changes in Strength, Joint Laxity, and Walking Patterns                                                       ...
Age-Related Changes in Strength, Joint Laxity, and Walking PatternsTable 2.Mean Values (Adjusted for Walking Speed) and 95...
Age-Related Changes in Strength, Joint Laxity, and Walking Patternspose the joint to articular cartilagedamage. A failure ...
Age-Related Changes in Strength, Joint Laxity, and Walking Patternswould be required to further investi-       means to ma...
Age-Related Changes in Strength, Joint Laxity, and Walking Patternsmay suggest why they did not de-                 the Sc...
Age-Related Changes in Strength, Joint Laxity, and Walking Patterns28 Moore TM, Meyers MH, Harvey JP Jr. Col-       35 Ben...
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Age related change in strength, joint laxity, and walking patterns. are they related to knee oa

  1. 1. Research Report Age-Related Changes in Strength, Joint Laxity, and Walking Patterns: Are They Related to Knee Osteoarthritis? Katherine S Rudolph, Laura C Schmitt, Michael D LewekKS Rudolph, PT, PhD, is AssistantProfessor, Department of PhysicalTherapy and Program in Biome- Background and Purposechanics and Movement Science, Aging is associated with musculoskeletal changes and altered walking patterns. TheseUniversity of Delaware, 301 changes are common in people with knee osteoarthritis (OA) and may precipitate theMcKinly Lab, Newark, DE 19716 development of OA. We examined age-related changes in musculoskeletal structures(USA). Address all correspondenceto Dr Rudolph at: krudolph@ and walking patterns to better understand the relationship between aging and OA.LC Schmitt, PT, PhD, is Post-Doctoral Fellow, Department of MethodsPediatrics, University of Cincin- Forty-four individuals without OA (15 younger, 15 middle-aged, 14 older adults) andnati, College of Medicine; and 15 individuals with medial knee OA participated. Knee laxity, quadriceps femorisPhysical Therapist, Sports Medi- muscle strength (force-generating capacity), and gait were assessed.cine Biodynamics Center, Cincin-nati Children’s Hospital MedicalCenter, Cincinnati, Ohio. ResultsMD Lewek, PT, PhD, is Assistant Medial laxity was greater in the OA group, but there were no differences between theProfessor, Center for Human middle-aged and older control groups. Quadriceps femoris strength was less in theMovement Science, Division of older control group and in the OA group. During the stance phase of walking, the OAPhysical Therapy, University of group demonstrated less knee flexion and greater knee adduction, but there were noNorth Carolina at Chapel Hill, differences in knee motion among the control groups. During walking, the olderChapel Hill, NC. control group exhibited greater quadriceps femoris muscle activity and the OA group[Rudolph KS, Schmitt LC, Lewek used greater muscle co-contraction.MD. Age-related changes instrength, joint laxity, and walkingpatterns: are they related to knee Discussion and Conclusionosteoarthritis? Phys Ther. 2007: Although weaker, the older control group did not use truncated motion or higher87:1422–1432.] co-contraction. The maintenance of movement patterns that were similar to the© 2007 American Physical Therapy subjects in the young control group may have helped to prevent development ofAssociation knee OA. Further investigation is warranted regarding age-related musculoskeletal changes and their influence on the development of knee OA. Post a Rapid Response or find The Bottom Line: www.ptjournal.org1422 f Physical Therapy Volume 87 Number 11 November 2007
  2. 2. Age-Related Changes in Strength, Joint Laxity, and Walking PatternsS ymptomatic knee osteoarthritis in the presence of quadriceps femo- ing that the material properties of (OA) is a worldwide problem1– 4 ris weakness, which occurs with ag- ligaments of older adults can lead to that produces substantial dis- ing,7–11 and in the presence of knee excessive joint laxity. Becauseability in middle-aged and older OA, either the hamstring or the gas- frontal-plane laxity has been relatedadults and leads to a tremendous trocnemius muscles may be required to high muscle co-contraction in in-economic burden on society.5 The to assist with knee control. dividuals with knee OA,24 it is plau-prevalence of OA among older indi- sible that normal age-related in-viduals has led some authors6 to re- Activation of muscles surrounding creases in joint laxity also maygard its development as a normal the knee can occur selectively and contribute to higher muscle co-part of aging. Loeser and Shakoor,6 with precise timing that allows for contraction patterns and predisposehowever, suggested that age-related normal knee motion, or, alterna- individuals to develop knee OA.changes in musculoskeletal tissue, tively, activation can occur more Whether older adults have greatersuch as muscle weakness and liga- generally as a global co-contraction frontal-plane knee laxity coupledment laxity, do not directly cause pattern that could limit joint motion. with higher muscle co-contraction isOA, but may predispose individuals We, therefore, have defined the not develop the disease. It is possible movement strategy that involves boththat the manner in which people re- increased muscle co-contraction and In this study, we investigated thespond to these age-related changes reduced knee flexion during walking knee laxity, quadriceps femoris mus-in musculoskeletal tissues about the as a “stiffening strategy.” Excessive cle strength (force-generating capac-knee may be related to whether or muscle co-contraction can lead to ity), walking patterns, and muscle ac-not OA develops in the knees of excessive joint contact forces,18 and tivation patterns in 3 age groups ofolder adults. reduced knee motion during weight people without symptomatic or ra- acceptance can cause higher impact diographic knee OA to examine fac-The features that are similar between loads in the knee.19,20 Older adults tors that are thought to contribute toolder adults and people with knee are known to walk with less knee the development of knee OA. TheOA include quadriceps femoris mus- flexion,21 but whether they do so results are discussed in relation tocle weakness and altered knee move- as a result of higher muscle co- characteristics of a group of peoplement during walking. Sarcopenia is contraction is unknown. However, with knee OA. Because the olderwell known in older adults and leads not all older adults develop knee OA. adults in our study did not have jointto quadriceps femoris muscle weak- If older adults who have not devel- degeneration, we hypothesized thatness,7–11 which has been noted in oped knee OA walk with a knee stiff- older adults who are healthy willpeople as early as 40 years of age.9 ening strategy, then the combination have weaker quadriceps femorisBecause both the development of of reduced knee flexion and muscle muscles and increased frontal-planeknee OA12 and quadriceps femoris co-contraction alone, in the pres- knee laxity but will not exhibitmuscle strength changes9 are initi- ence of quadriceps femoris muscle greater muscle co-contraction pat-ated during middle age, it is not sur- weakness, is unlikely to contribute terns compared with young orprising that quadriceps femoris mus- to the development of knee OA. middle-aged people.cle weakness has been implicated inthe development of knee OA.13–15 Another possible precursor to knee Method OA is excessive frontal-plane laxity, SubjectsQuadriceps femoris muscle weak- which is common in people with Fifty-nine people were recruitedness also is associated with adapta- existing knee OA.22–24 Specifically, from the community or were re-tions in walking patterns that are the- greater frontal-plane knee laxity is ferred by a local orthopedic surgeonorized to put articular cartilage at observed in both the involved and to participate in the study. All sub-risk. For instance, subjects with knee uninvolved knees of people with OA jects signed an informed consentOA who have weaker quadriceps compared with control subjects, sug- statement approved by the Humanfemoris muscles exhibit less stance- gesting that laxity may precede the Subjects Review Board of the Univer-phase knee motion during walking.16 development of knee OA.22 Addi- sity of Delaware. Forty-four partici-At self-selected walking speeds, it is tionally, a significant correlation be- pants who reported no history ofthe role of the quadriceps femoris tween frontal-plane laxity and age knee OA (confirmed by radiograph)muscles to control knee flexion dur- has been observed in individuals or previous lower-extremity injurying weight acceptance while the without evidence of knee OA.22 This comprised 3 control groups (15hamstring and gastrocnemius mus- finding is consistent with the find- younger individuals [ages 18 –25cles are typically silent.17 However, ings of other studies,22,25,26 indicat- years], 15 middle-aged individualsNovember 2007 Volume 87 Number 11 Physical Therapy f 1423
  3. 3. Age-Related Changes in Strength, Joint Laxity, and Walking PatternsTable 1.Group Characteristics Young Middle-aged Older Osteoarthritis Control Group Control Group Control Group Group (n 15) (n 15) (n 14) (n 15) Age (y), X (range) 20.6 (18–25) 49.2 (40–57) 68.8 (60–80) 49.2 (39–57) Sex (female/male) 8/7 7/8 10/4 7/8 2 a,b a c Body mass index (kg/m ), X (SD) 24.3 (2.8) 28.7 (5.5) 24.7 (2.5) 30.7 (4.8)b.c Alignment (°), X (SD) Not tested 0.1 (1.58)d valgus 1.0 (2.09)d varus 6.33 (2.39)d varusa P .030.b P .001.c P .002.d P .001.[ages 40 –59 years], and 14 older in- anterior (approximately 30° of knee was assessed by repeated testing ondividuals [ages 60 – 80 years]) flexion) radiographs of the knees of a subset of 8 subjects and showed(Tab. 1). The middle-aged individuals the middle-aged and older control high reliability for medial (intraclasswere matched by age and sex to 15 groups were obtained as an added correlation coefficient [ICC] .96)people with symptomatic, medial precaution to rule out the presence and lateral laxity (ICC .98).knee OA (Tab. 1). The subjects with of knee OA. Radiographs were notmedial knee OA were part of a larger taken of the knees of the young sub-study of people who were going to jects because they had no kneeundergo a high tibial osteotomy. symptoms and no history of kneeThey had no history of knee liga- injury and were unlikely to have un-ment injury; however, those individ- diagnosed knee OA based on theuals with a history of meniscectomy above definition.were included. Data on some ofthe people with knee OA and data Varus and valgus stress radiographson the middle-aged control group were taken of the tested lower ex-have been reported previously.24 tremity in the middle-aged and olderRadiographic information, isometric control groups as well as the OAquadriceps femoris strength, and ki- group. Subjects were positioned su-nematic, kinetic, and electromyo- pine on a radiograph table with thegraphic (EMG) data during walking knee flexed to 20 degrees and thewere collected from the more- patella facing anteriorly. The x-rayinvolved limb of the subjects with tube was centered approximatelyOA and a randomly chosen limb of 100 cm above the knee joint. Athe control subjects. The test limb of TELOS* stress device was used to ap-the control subjects was chosen ran- ply a 150-N force in the varus ordomly to avoid any possible influ- valgus direction (Fig. 1). Medial andence of limb dominance. lateral joint spaces were measured at the narrowest location in bothProcedure compartments using calipers. X-rayRadiographs. The diagnosis of OA beams were adjusted for magnifica- Figure based on the presence of knee tion using a known distance from the Setup for stress radiographs. The top im-pain in conjunction with age over 50 TELOS device that was visible in ev- ages show the limb alignment in theyears and either radiographic evi- ery image. Medial and lateral joint TELOS device (top left) and the resultingdence of OA (eg, osteophytes) or laxities were calculated as described radiograph (top right), and the method ofother symptoms such as stiffness or in Figure 1.28 Interrater reliability calculating medial laxity is shown in the lower images. Lateral laxity was calculatedcrepitus.27 Although none of our similarly but with subtraction of the lateralcontrol subjects complained of knee * Austin & Associates, 1109 Sturbridge Rd, joint space in valgus from lateral jointpain or stiffness, standing posterior- Fallston, MD 21047. space in varus.1424 f Physical Therapy Volume 87 Number 11 November 2007
  4. 4. Age-Related Changes in Strength, Joint Laxity, and Walking PatternsSkeletal alignment of the tested limb tion was measured as the highest sampled at 1,920 Hz. Ground reac-was measured with a standing long volitional force (N) during the con- tion force data were used to calcu-cassette radiograph for the middle- traction and was normalized to body late moments about the knee and foraged and older control groups and mass index (BMI) (N/BMI). In tests determination of heel-strike andthe OA group. Subjects stood, with- on 10 subjects who were healthy, toe-off.out footwear, with the tibial tuber- repeated testing of the MVIC re-cles facing forward and the x-ray vealed an intraclass correlation coef- Electromyographic data were col-beam centered at the knee from a ficient (2,1) of .98.33 lected with a 16-channel electromyo-distance of 2.4 m. Alignment was graphy system (model MA-300-16#)measured as the angle formed by the Gait and electromyographic sampled at 1,920 Hz. After skin prep-intersection of the mechanical axes (EMG) data. To determine knee aration, surface electrodes with par-of the femur and tibia.29 –31 A knee motion during walking, the motions allel, circular detection surfaceswas in varus alignment when the in- of the lower-extremity segments (1.14 cm in diameter, 2.06 cm apart),tersection of the lines was 0 de- were collected by a 6-camera, pas- a common mode rejection ratio (100grees in the varus direction and was sive, 3-dimensional motion analysis dB at 65 Hz), and a signal detectionin valgus alignment when the inter- system (Vicon 512)§ at 120 Hz. Cam- range of less than 2 V for thesection of the lines was 0 degrees eras were calibrated to detect mark- built-in preamplifier were placedin the valgus direction.30 ers within a volume that was 1.5 over the mid-muscle bellies of the 2.4 1.5 m. Calibration residuals lateral quadriceps femoris (LQ), me-Quadriceps femoris muscles func- were kept below 0.6 mm. The cam- dial quadriceps femoris (MQ), lateraltion. Quadriceps femoris muscle eras detected retroreflective markers hamstring (LH), medial hamstringforce output was measured with an (2.5 cm in diameter) placed on the (MH), lateral gastrocnemius (LG),isokinetic dynamometer (Kin-Com tested lower extremity. Markers and medial gastrocnemius (MG) mus-500H).† Each subject sat with the were placed bilaterally over the cles. Electromyographic data wereknee and hip flexed to 90 degrees, greater trochanters, the lateral femo- recorded for 2 seconds at rest andthe knee joint axis aligned with the ral condyles, and lateral malleoli for during an MVIC for each muscledynamometer axis, and the trunk identification of appropriate joint group for normalization.fully supported. Thigh and hip straps centers. Thermoplastic shells with 4secured each subject in the seat, rigidly attached markers were used Motion, force, and EMG data werewhile an ankle strap secured the to track segment motion. The shells collected simultaneously as subjectsshank to the dynamometer. Subjects were secured on the posterior-lateral walked at a self-selected speed alongperformed a maximal volitional iso- aspects of the thigh and shank. Pre- a 9-m walkway for 10 trials. Walkingmetric contraction (MVIC) on which vious work in our laboratory (unpub- speed was recorded from 2 photo-a supramaximal burst of electrical lished data collected April 2002) has electric beams to ensure that speedcurrent (Grass S48 stimulator‡) (100 revealed good reliability for kine- did not vary more than 5% from theirpulses/second, 600-microsecond matic variables with ICCs ranging self-selected speed during the trials.pulse duration, 10-pulse tetanic from .6343 to .9969. The ICCs for Trials were only accepted if the sub-train, 130 V) was applied. The burst the kinematic variables used in the ject walked at a consistent speed andsuperimposition was used for the present study ranged from .9721 to walked across the force platformmeasurement if the subjects were .9969. Errors in estimating bone without adjusting their stride in anyproviding maximum activation of movement from skin mounted mark- way to contact the force platform.the quadriceps femoris muscles.32 A ers for sagittal and frontal plane mo-central activation ratio (CAR) is a ra- tions are approximately 2 to 3 de- Data management. Marker tra-tio between the highest volitional grees during the stance phase of jectories and ground reaction forcesforce (measured as the peak force walking.34,35 Vertical, medial-lateral, were collected over the stance phasebefore the electrical burst was ap- and anterior-posterior ground reac- of one limb (heel-strike to toe-offplied) and the force achieved during tion forces were collected from a on the force platform) and were fil-the electrically elicited burst. Maxi- 6-component force platform (Bertec tered with a second-order, phase-mum volitional isometric contrac- force platform, model 60905 ) and corrected Butterworth filter with a cutoff frequency of 6 Hz for the† Isokinetic International, 6426 Morning Glory video data and 40 Hz for the force-Dr, Harrison, TN 37341. §Oxford Metrics, 14 Minns Business Park,‡ Grass Instrument Division, Astro-Med Inc, West Way, Oxford OX2 0JB, United Kingdom.600 East Greenwich Ave, West Warwick, RI Bertec Corp, 6171 Huntley Rd, Ste J, Colum- # Motion Lab Systems, 15045 Old Hammond02893. bus, OH 43229 Hwy, Baton Rouge, LA 70816.November 2007 Volume 87 Number 11 Physical Therapy f 1425
  5. 5. Age-Related Changes in Strength, Joint Laxity, and Walking Patternsplate data. Sagittal- and frontal-plane contraction was operationally de- group (P .030), and subjects in theknee angles and external knee mo- fined as the simultaneous activation OA group had higher BMI valuesments were calculated with Euler of a pair of opposing muscles and than the subjects in the young andangles and inverse dynamics, respec- was calculated using an equation de- older control groups (P .002)tively (Visual 3D**). Data were ana- veloped in our laboratory37: (Tab. 1). The knees of the subjects inlyzed using custom-written com- the middle-aged and older controlputer programs based on strict Average co-contraction value groups were in less varus than thecriteria (eg, thresholds for initial con- n knees of the subjects in the OAtact, time of peak adduction mo- lowerEMGi lowerEMGi higherEMGi group (P .001) (Tab. 1). higherEMGiment) to eliminate tester bias. Data i 1were analyzed during the loading in- n Knee Laxityterval, which we defined as from 100 Subjects in the OA group had signif-milliseconds prior to initial contact where i is the sample number and n icantly greater medial laxity than the(to account for electromechanical is the total number of samples in the subjects in the middle-aged and olderdelay)36 through the first peak knee interval. Co-contraction values were control groups (P .001) (Fig. 2).adduction moment. Data during the averaged across the trials, and the There were no differences in lateralloading interval were time normal- average was used for analysis. This laxity between the subjects in theized to 100 data points and averaged method does not identify which OA group and the subjects in theacross each subject’s trials. Knee mo- muscle is more active; rather, it rep- middle-aged and older controlments were normalized to body resents a relative activation of 2 mus- groups (P .272) (Fig. 2).mass height and are expressed as cles while accounting for the magni-external moments. In addition to dis- tudes of both muscles. Co- Quadriceps Femoriscrete variables, we calculated knee contraction was calculated between Muscle Strengthflexion excursion (from initial con- the LQ and LH (LQH), MQ and MH The subjects in the young controltact to peak knee flexion) and knee (MQH), LQ and LG (LQG), and MQ group produced greater volitionaladduction excursion during loading. and MG (MQG) muscles. quadriceps femoris muscle force than the subjects in the older controlAll EMG data were band-pass filtered Data Analysis group (P .001) or the subjects infrom 20 to 350 Hz. A linear envelope Group means and standard devia- the OA group (P .001) (Fig. 3). Sub-was created with full-wave rectifica- tions were calculated for all data. jects in the middle-aged controltion and filtering with a 20-Hz low- One-way analysis of variance group generated more force than thepass filter (eighth-order, phase- (ANOVA) was used to detect group subjects in the older control groupcorrected Butterworth filter). The differences in BMI, quadriceps fem- (P .002) or the subjects in the OAlinear envelope was normalized to oris muscle strength and CAR, and group (P .003) (Fig. 3). There werethe maximum EMG signal obtained radiograph variables. Because walk- no differences between the sub-during a MVIC for each muscle. ing speed can influence lower- jects in the older control group and extremity kinematic and kinetic the subjects in the OA groupCustom-designed software (Labview, data,38 – 40 analysis of covariance (AN- (P 1.0) or between the subjects inversion 8.0††), using the same kine- COVA), with walking velocity as a the young and middle-aged controlmatic and kinetic events as stated covariate, was used to detect group groups (P .974) (Fig. 3). No dif-above, was used to analyze all EMG differences in kinematic and kinetic ferences in CAR were observeddata. Magnitude of muscle activity variables. For strength, radiograph, among the control groups (youngand co-contraction between oppos- and kinematic and kinetic data, sig- 0.93 .038 [X SD], middle-ageding muscle groups were analyzed nificance was established when 0.93 .027, older 0.94 .052; P .84).over the loading interval after it was P .05. To detect group differencestime normalized to 100 points. Mag- in magnitudes of muscle activity and Gait Characteristicsnitude of muscle activity was ex- in co-contraction variables, 95% con- The subjects in the middle-aged con-pressed as the average rectified value fidence intervals were used to evalu- trol group walked faster than theacross the loading interval. Co- ate differences in the mean values. subjects in the OA group (P .023) and there were no other statistical Results differences among the groups** C-Motion Inc, 15821-A Crabbs Branch Way, Subjects in the middle-aged control (young control group 1.39 0.08Rockville, MD 20855.†† National Instruments, 11500 N Mopac group had greater BMI values than [X SD] m/s, middle-aged controlExpwy, Austin, TX 78759-3504. the subjects in the young control group 1.51 0.15 m/s, older con-1426 f Physical Therapy Volume 87 Number 11 November 2007
  6. 6. Age-Related Changes in Strength, Joint Laxity, and Walking Patterns groups, but was reduced in subjects in the OA group compared with the subjects in the young (P .006) and older (P .039) control groups. There were no differences in frontal- plane knee motions or moments among the young, middle-aged, and older control groups. The subjects in the OA group exhibited greater ad- duction compared with the subjects in the young, middle-aged, and older control groups at initial contact (P .004) and at peak adduction dur- ing loading (P .001). The OA group showed greater adduction excursion compared with the young control group (P .049) and the older con- trol group (P .055); however, theFigure 2. latter was not statistically significantMedial and lateral joint laxity. MA middle-aged control group, O older control group, at the P .05 level. The OA groupOA group with osteoarthritis. * P .001. Error bars represent standard deviation. showed greater peak knee adduction moments compared with the young, middle-aged, and older control groups (P .002). Muscle Activity There was a large degree of variabil- ity in the muscle activation and co- contraction as is evident in the large range of the 95% confidence inter- vals shown in Figures 4 and 5. Dur- ing loading response, there was a tendency for the subjects in the older control group to use higher lateral quadriceps femoris activity than the subjects in the young and middle-aged control groups and a tendency for higher medial gastroc- nemius muscle activity in the sub- jects in the OA group and the older control group than in the subjects inFigure 3. the young and middle-aged controlQuadriceps femoris muscle force production. Y young control group, MA middle- groups. However, the overlap of theaged control group, O older control group, OA group with osteoarthritis, 95% confidence intervals indicateN/BMI highest volitional force during contraction normalized to body mass index. that a larger sample size is needed to* P .000, † P .000, ‡ P .002, § P .003. Error bars represent standard deviation. determine with more certainty whether the population means aretrol group 1.45 0.10 m/s, OA older control groups, but the OA different. In terms of muscle co-group 1.38 0.12 m/s). group showed less knee flexion ex- contraction, there were no differ- cursion compared with all 3 control ences among the control groups, al-Results of kinematic and kinetic vari- groups (P .036). The peak knee though the OA group showed higherables are shown in Table 2. Knee flexion moment was no different co-contraction than the subjects inflexion excursion was not different among the subjects in the young, the young control group in the LQGamong the young, middle-aged, and middle-aged, and older control and MQG muscle pairs (Fig. 5).November 2007 Volume 87 Number 11 Physical Therapy f 1427
  7. 7. Age-Related Changes in Strength, Joint Laxity, and Walking PatternsTable 2.Mean Values (Adjusted for Walking Speed) and 95% Confidence Interval (in Parentheses) for Sagittal- and Frontal-PlaneKinematics and Kinetics Young Middle-aged Older Osteoarthritis Group P Control Group Control Group Control Group (n 15) (n 15) (n 15) (n 14) Kinematics (°) Sagittal-plane knee angle 4.97 ( 7.76, 2.18) 3.59 ( 6.48, 0.70) 5.56 ( 8.41, 2.70) 4.68 ( 7.50, 1.85) .800 at initial contact (negative is flexion) Knee flexion excursion 16.75 (14.42, 19.09) 16.97 (14.55, 19.39) 17.94 (15.55, 20.33) 11.98 (9.62, 14.35) .036a during loading Frontal-plane knee angle 0.434 ( 2.5, 1.64) 2.30 ( 4.45, 0.15) 0.833 ( 2.96, 1.29) 4.83 (2.73, 6.93) .004a at initial contact (positive is adduction) Peak frontal-plane knee 2.62 (0.40, 4.84) 2.35 (0.05, 4.65) 2.18 ( 0.10, 4.45) 9.93 (7.68, 12.18) .001a angle during loading (positive is adduction) Knee adduction 3.06b (1.99, 4.12) 4.65 (3.54, 5.76) 3.00c (1.92, 4.10) 5.10b,c (4.02, 6.18) .049b excursion during .055 loading Kinetics (N m/kg m) Peak knee flexion 0.36b ( 0.29, 0.44) 0.27 ( 0.19, 0.35) 0.33c ( 0.25, 0.41) 0.17b,c ( 0.09, 0.25) .006b moment during .039c loading Peak knee adduction 0.28a (0.23, 0.32) 0.33a (0.28, 0.37) 0.26a (0.21, 0.31) 0.45a (0.41, 0.50) .002a moment during loadinga Osteoarthritis group different from all control groups.b Osteoarthritis group different than young control group.c Osteoarthritis group different than older control group.Discussion and Conclusions tablish an environment in which OA sample size, these findings suggestMost studies of age-related differ- could develop. The results set the that the older adults included in thisences in movement and muscle acti- stage for future research into how study demonstrate movement strate-vation patterns include samples of age-related musculoskeletal changes gies similar to those of younger indi-young subjects in their 20s and older might influence the development of viduals, which may have helpedadults over 60 years of age; yet, age- knee OA. to prevent the development ofrelated changes in characteristics knee OA as they aged; these find-such as muscle strength or neuro- The results of this study indicate that ings, however, warrant furthermuscular responses can occur in healthy aging was associated with a investigation.middle age7–11 and may coincide considerable loss of quadriceps fem-with the development of knee OA. oris muscle strength in the older As age-related muscle weakness de-As a result, we intended to investi- adults, although we did not observe velops, individuals must adapt theirgate characteristics in individuals increased frontal-plane laxity in movements and muscle activity pat-who are healthy that are purported those subjects. Despite quadriceps terns to accommodate the dimin-to be associated with the develop- femoris muscle weakness, the older ished force-generating capacity ofment of knee OA across a range of adults participating in this study did their aging muscles to maintain a cer-ages, including middle age. The not adopt a knee stiffening strategy tain level of function. As such, wenovel nature of this approach and (ie, reduced knee motion and high propose that adaptations allowingthe findings of this study provide muscle co-contraction) that we spec- for the continuation of normalizedsome insights into how changes in ulate may contribute to damage of joint mechanics and muscle activa-musculoskeletal function might es- articular cartilage. Despite the small tion patterns are less likely to predis-1428 f Physical Therapy Volume 87 Number 11 November 2007
  8. 8. Age-Related Changes in Strength, Joint Laxity, and Walking Patternspose the joint to articular cartilagedamage. A failure to adapt tostrength declines might contributeto the development of movementpatterns similar to individuals withquadriceps femoris muscle weak-ness due to knee joint patholo-gy.41– 43 Because the older adults inthis study exhibited similar move-ment and muscle activity patterns tothose in the younger age groups, itappears that they have discovered asuccessful approach to maintainingnormal knee function despite theirquadriceps femoris muscle strengthdecline.In particular, the older control sub-jects exhibited significantly weakerquadriceps femoris muscles com-pared to the younger cohorts, yetthey showed no differences in knee Figure 4.motion during weight acceptance Mean electromyographic (EMG) muscle activation during loading and 95% confidencecompared with the young control interval (indicated by bars). MVIC maximal voluntary isometric contraction, LQ lateral quadriceps femoris muscle, MQ medial quadriceps femoris muscle,subjects. Quadriceps femoris muscle LH lateral hamstring muscle, MH medial hamstring muscle, LG lateral gastrocne-weakness has previously been asso- mius muscle, MG medial gastrocnemius muscle.ciated with reduced knee motionduring walking in the presence ofjoint pathology.33,44 Electromyo-graphic data suggest that the olderadults in this study have compen-sated for the quadriceps femorismuscle weakness by selectively in-creasing quadriceps activity duringloading. Although adequate muscleactivity is necessary to ensure jointstability, too much activation can re-sult in limited knee flexion and in-creased impact load on the knee.19Whether increased activation wouldbe a positive or negative adaptationduring walking, therefore, would de-pend on the end result of the muscleactivity. The older adults in thisstudy were able to maintain normal-ized knee motion, comparable toyounger subjects, with increasedquadriceps femoris activity. The abil-ity to maintain normalized knee jointmechanics may have contributed tothe lack of knee OA in this older Figure 5. Mean muscle co-contraction index during loading and 95% confidence interval (indi-adult cohort. Our conclusions are cated by bars). LQH lateral quadriceps femoris-lateral hamstring, MQH medial quad-limited by the cross-sectional design riceps femoris-medial hamstring, LQG lateral quadriceps femoris-lateral gastrocne-of this study. A longitudinal study mius, and MQG medial quadriceps femoris-medial gastrocnemius muscle pairs.November 2007 Volume 87 Number 11 Physical Therapy f 1429
  9. 9. Age-Related Changes in Strength, Joint Laxity, and Walking Patternswould be required to further investi- means to maintain normal move- muscle co-contraction strategies.41,43gate the effect of age-related muscu- ment strategies. Additional research is required to de-loskeletal changes on movement lineate whether consistent differ-strategies in terms of the develop- The similarity in the knee motion ences in muscle activation patternsment of knee OA. among the control groups might be exist in people with knee OA or unexpected because other research- whether there are several strategiesDespite prior evidence of reduced ers21 have shown that older adults that people use to help control thestiffness and ligament strength with walk with less knee motion during knee in the face of a pathologic con-advancing age,25 we were unable to loading when walking at the same dition. Whether one strategy is moredetect increases in frontal plane lax- speed as younger subjects. It is pos- detrimental than another remains toity with aging in the control subjects. sible that our finding of similar be seen and should be furtherThe OA group, however, exhibited sagittal-plane knee kinematics investigated.increased frontal-plane laxity. Al- among the young, middle-aged, andthough subjects were carefully older control groups is due to a small There are several limitations to thescreened for a history of ligament number of subjects in our sample or study design that the readers shouldinjury, we included individuals with related to our method of subject re- take into consideration. First, testersa history of meniscal damage in the cruitment. Some of the older adults were not blinded to group assign-OA group. The subjects with OA had in our study were recruited from lo- ment, which may have created biasno history of an incident ligamentous cal fitness and senior centers and in recording data. However, the useinjury, and studies45,46 suggest that may represent a more active older of the TELOS device to apply uni-meniscal injury in the absence of a adult compared with a typical older form stress during the stress radio-traumatic event is a part of the de- adult, and this may have enabled the graphs reduced the influence ofgenerative process of knee OA. In older subjects in our study to better tester bias for this measure. Testersindividuals with knee OA, the pres- control more knee motion as the attempted to provide equivalent ver-ence of increased frontal plane laxity limb accepted weight. Future studies bal encouragement to all subjectsis known to degrade the relationship may consider measuring daily activ- equally when testing quadricepsbetween strength and physical ity levels to account for potential in- femoris muscle strength. In addition,function.47 fluences on walking speeds and the discomfort of the superimposed movement patterns. burst was motivation for all subjectsBecause the older adults who were to perform to their best ability tohealthy did not have to cope with It is interesting to note that differ- avoid repeat testing. During thestrength loss in a lax joint, they may ences in muscle co-contraction val- movement analysis testing, similarhave had the ability to adopt move- ues were found only between the instructions were provided to allment strategies that remain normal- subjects with OA and young control subjects to walk at a comfortableized and may be “joint sparing.” We subjects. In this study, the subjects speed. Custom-written computer al-can speculate that the subjects with with OA used greater lateral gas- gorithms were used to determineOA did not have such an option, be- trocnemius muscle activity during data points used in the analysis ofcause they had to contend with loading and greater quadriceps kinematics, kinetics, and EMG datastrength loss in a lax joint, making femoris-gastrocnemius muscle co- to reduce tester bias. Second, thejoint stabilization a primary determi- contraction on the medial and lateral distribution of male and female sub-nant in their adopted control strat- sides compared with the young con- jects in the groups was not the sameegy. These findings suggest that trol subjects, but no differences and we did not account for the levelquadriceps femoris muscle weak- were observed between the subjects of physical activity in the subjects inness is associated with reduced with OA and the middle-aged control each group, both of which couldstance-phase knee motion in the subjects. This is in contrast to other have influenced the results. Finally,presence of other factors, such as work in our lab in which subjects the subjects all walked faster thanincreased knee laxity or pain, as was with OA were found to use higher has been reported elsewhere,48 andevident in the OA group. Such a co-contraction between the quadri- walking speed—although used as aspeculation would suggest that age- ceps femoris-gastrocnemius muscles covariate—may have influenced therelated changes to musculoskeletal on the medial side only compared results.tissues alone are insufficient to lead with age-matched control subjects.24to the development of knee OA, pro- It is possible that people with patho- The finding that the older adults invided the aging individual has the logic conditions in the knee may our study used what can be consid- limit knee motion through different ered a favorable movement pattern1430 f Physical Therapy Volume 87 Number 11 November 2007
  10. 10. Age-Related Changes in Strength, Joint Laxity, and Walking Patternsmay suggest why they did not de- the Science of Joint Preservation Course, Uni- 13 Slemenda C, Brandt KD, Heilman DK, et al. versity of Louisville, Louisville, Ky, April 28 – Quadriceps weakness and osteoarthritis ofvelop knee OA. We speculate that the knee. Ann Intern Med. 1997;127: 29, 2006.the manner in which middle-aged in- 97–104.dividuals compensate for age-related The contents of this article are solely the 14 Brandt KD, Heilman DK, Slemenda C, et al. responsibility of the authors and do not nec- Quadriceps strength in women with radio-neuromuscular changes might influ- graphically progressive osteoarthritis of essarily represent the official views of theence the future integrity of the the knee and those with stable radio- NCRR or NIH. graphic changes. J Rheumatol. 1999;26:knee’s articular cartilage. An alterna- 2431–2437.tive interpretation of our results is This article was submitted May 12, 2006, and 15 Hurley MV. The role of muscle weakness was accepted July 11, 2007.that the process of knee OA may in the pathogenesis of osteoarthritis. Rheum Dis Clin North Am. 1999;25:283–cause changes in movement and DOI: 10.2522/ptj.20060137 298, vi.muscle activation patterns. The ab- 16 Bennell KL, Hinman RS, Metcalf BR. Asso-sence of reduced knee motion and References ciation of sensorimotor function with knee joint kinematics during locomotionhigher co-contraction in the middle- 1 Carmona L, Ballina J, Gabriel R, Laffon A; in knee osteoarthritis. Am J Phys Med Re- EPISER Study Group. The burden ofaged and older control subjects may musculoskeletal diseases in the general habil. 2004;83:455– 463; quiz 464 – 456, 491.have been a consequence of not hav- population of Spain: results from a na- tional survey. Ann Rheum Dis. 2001;60: 17 Perry J. 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J Biomech. 1996;29: 1987;46:804 – 808. 1523–1529. 4 McAlindon TE, Wilson PW, Aliabadi P, et 20 Cook TM, Farrell KP, Carey IA, et al. Ef-Dr Rudolph and Dr Schmitt provided writing al. Level of physical activity and the risk of fects of restricted knee flexion and walk-and project management. Dr Schmitt and Dr radiographic and symptomatic knee osteo- ing speed on the vertical ground reaction arthritis in the elderly: the Framingham force during gait. J Orthop Sports PhysLewek provided data collection. All authors study. Am J Med. 1999;106:151–157. Ther. 1997;25:236 –244.provided data analysis. Dr Rudolph provided 5 Peat G, McCarney R, Croft P. Knee pain 21 DeVita P, Hortobagyi T. Age causes a re-fund procurement, facilities/equipment, and and osteoarthritis in older adults: a review distribution of joint torques and powersinstitutional liaisons. Dr Lewek provided con- of community burden and current use of during gait. J Appl Physiol. 2000;88:sultation (including review of manuscript be- primary health care. Ann Rheum Dis. 1804 –1811.fore submission). The authors acknowledge 2001;60:91–97. 22 Sharma L, Lou C, Felson DT, et al. Laxity inWilliam Newcomb, MD, for providing sub- 6 Loeser RF, Shakoor N. Aging or osteoar- healthy and osteoarthritic knees. Arthritisject recruitment and Laurie Andrews, RTR, thritis: which is the problem? Rheum Dis Rheum. 1999;42:861– 870. Clin North Am. 2003;29:653– 673. 23 Wada M, Imura S, Baba H, Shimada S. Kneefor assistance with radiographs. 7 Akima H, Kano Y, Enomoto Y, et al. Mus- laxity in patients with osteoarthritis andThis study was approved by the Human cle function in 164 men and women aged rheumatoid arthritis. Br J Rheumatol.Subjects Review Board of the University 20 – 84 yr. Med Sci Sports Exerc. 2001;33: 1996;35:560 –563. 220 –226. 24 Lewek MD, Rudolph KS, Snyder-Macklerof Delaware. 8 Frontera WR, Hughes VA, Lutz KJ, Evans L. Control of frontal plane knee laxity dur- This study was funded, in WJ. A cross-sectional study of muscle ing gait in patients with medial compart- strength and mass in 45- to 78-yr-old men ment knee osteoarthritis. Osteoarthritis part, by a grant (P20- and women. J Appl Physiol. 1991;71: Cartilage. 2004;12:745–751. RR16458) from the Na- 644 – 650. 25 Noyes FR, Grood ES. The strength of the tional Center for Research 9 Lindle RS, Metter EJ, Lynch NA, et al. Age anterior cruciate ligament in humans andResources (KSR), a component of the Na- and gender comparisons of muscle Rhesus monkeys. J Bone Joint Surg Am.tional Institutes of Health (NIH); a grant strength in 654 women and men aged 1976;58:1074 –1082.(T32HD007490) from the NIH (LCS, MDL); a 20 –93 yr. J Appl Physiol. 1997;83: 26 Woo SL, Hollis JM, Adams DJ, et al. TensilePODS II grant from the Foundation for Phys- 1581–1587. properties of the human femur-anteriorical Therapy (LCS, MDL); and a Doctoral Re- 10 Roos MR, Rice CL, Connelly DM, Vander- cruciate ligament-tibia complex: the ef- voort AA. Quadriceps muscle strength, fects of specimen age and Grant from the American College of contractile properties, and motor unit fir- Am J Sports Med. 1991;19:217–225.Sports Medicine (MDL). ing rates in young and old men. Muscle 27 Altman R, Asch E, Bloch D, et al. Develop- Nerve. 1999;22:1094 –1103. ment of criteria for the classification andThis work was presented as a platform pre- 11 Hurley MV, Rees J, Newham DJ. Quadri- reporting of osteoarthritis: classification ofsentation at the Combined Sections Meeting ceps function, proprioceptive acuity and osteoarthritis of the knee. Diagnostic andof the American Physical Therapy Associa- functional performance in healthy young, Therapeutic Criteria Committee of thetion; February 14, 2003; Tampa, Fla; as a middle-aged and elderly subjects. Age Age- American Rheumatism Association. Ar-platform presentation at XVth Biannual In- ing. 1998;27:55– 62. thritis Rheum. 1986;29:1039 –1049.ternational Society of Electrophysiology and 12 Felson DT, Zhang Y. An update on theKinesiology Conference; June 20, 2004; Bos- epidemiology of knee and hip osteoarthri-ton, Mass; and at the Functional Fitness and tis with a view to prevention. Arthritis Rheum. 1998;41:1343–1355.November 2007 Volume 87 Number 11 Physical Therapy f 1431
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